1. Field of the Invention
The invention relates to an element for fixing construction elements on wall and roof coverings, made of materials of low inherent strength, in particular insulation coverings, e.g. rigid foamed plastic, and more particularly to a fixing element having a basic body made of plastic bearing an external thread.
2. State of the Prior Art
In rooms which have wall coverings made of materials of low inherent strength, e.g. cooling rooms or the like which have inside coverings made of insulation material, the problem arises that, after installing the wall covering, objects have to be mounted on a wall or on the ceiling of the room, such as for example switching and control equipment, lighting fixtures or, for example, even panels, for example made of aluminum or plastic, for the panelling of the wall covering. Since the material used for the wall covering, e.g. rigid foamed polyurethane, has a low inherent strength, and thus known elements for fixing construction elements cannot grip firmly, each construction element to be mounted in a room with covered walls has to be mounted using relatively complex substructures, e.g. using L-bars, which are passed through the insulation layer and connected to the masonry of the room. However, the wall covering is then pierced by substructures of this type. By this means, in the case of the wall covering being, for example, an insulation covering, undesired hot and cold thermal bridges occur; in particular in cooling or refrigeration rooms, a water vapor block is applied under the insulation covering. Due to the substructures necessary for fixing construction elements which pierce the wall covering, this water vapor block is impaired in its function at places where elements for fixing are passed through the insulation covering.
It is true that an element constructed as a plug with an external thread is known according to DE-A-2,256,938. However, this serves for fixing heavy objects on walls made of, for example, plaster which, compared with insulation coverings, still have higher loading capacity. The known element constructed as a plug can be screwed with a positive fit into a borehole provided for this purpose, its external thread constructed as a self-cutting thread being intended to be screwed into the borehole into the material of the wall with removal of wall material. The known element is not suitable for anchorage in wall coverings made of relatively soft insulation material, e.g. rigid foamed polyurethane. It always requires a prefabricated borehole, by which the strength of the structure of the wall material is weakened from the very start. Moreover, a borehole has the disadvantageous effect of reducing the insulation function of a wall covering. Since the self-cutting thread of the known element also removes wall material in the surroundings of the borehole while it is being screwed into the borehole, a further weakening of the material structure also takes place which makes the known elements unsuitable for the applications described above. Moreover, the known element harbors the disadvantage that is can only be screwed into the assigned borehole using special tools.